A standard motor vehicle has a body provided with at least one generally horizontal rail having a bent end portion and along which a sliding door is displaceable between a closed position in against the body and an open position out from the body. Such a sliding-door assembly is typically provided on minivans intended for passenger use as the back doors, as they allow the passengers in and out of the vehicle through a large opening yet, since the door even when open is relatively close to the vehicle, the vehicle can be relative close to other vehicles or structures while still allowing back-door access.
Normally as the door is opened it moves first outward somewhat, then back along the side of the vehicle. When closed it slides forward and, at the end of its travel, moves inward to fit flush with the vehicle side. To this end the tracks normally have bent-in front ends in which carriages fixed to the door ride.
To prevent air leaks it is essential that the door be closed very tight. Thus its peripheral seal is compressed all around the door. In a manual system this means that the door must be pushed to with considerable force. In a power-closing and-opening system such as described in U.S. Pat. Nos. 5,140,316 and 5,316,365 it therefore becomes necessary to provide a fairly robust closing system to bring the necessary force to bear. For opening there is little problem, as once the latch is released the door pops out as the seal decompresses, but for closing it is necessary to bring enough force to bear that the seal can be compressed all around the door.
Thus these systems use an annular loop of cable that is operated wholly in tension by means of a relatively powerful motor so that it can bring the necessary force to bear. Alternately two different cables are used, one for opening and one for closing, and once again the cables are only effective in tension. During opening one of the cables is passive and during closing the other is passive.